In pipeline operation, starting and stopping a pump or opening or closing a valve will produce a surge in pressure which, under certain circumstances, could build up to dangerous proportions and may cause severe pipeline damage. In some pipeline installations, valves are provided which open at a predetermined, dangerously high pressure. However, such valves are necessarily installed at locations along the pipeline where surges are likely to be of greatest intensity, e.g., at the bottom of a steep grade, and not necessarily at locations convenient for inspection and servicing.
Generally, such valves relieve a pipeline surge by dumping the surge-producing flow into a reservoir from which the fluid must subsequently be removed. Accordingly, it is desirable to avoid dumping the fluid to the reservoir unless the surge is a potentially harmful one. For example, the shut-down of a single pump at a pumping station will ordinarily produce a surge, but the intensity of the surge may be well within the design capabilities of the pipeline.